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20 August 2009 Temperature dependence of hot carrier relaxation in PbSe nanocrystals: an ab initio study
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Temperature dependent dynamics of phonon-assisted relaxation of hot carriers, both electrons and holes, is studied in a PbSe nanocrystal using ab initio time-domain density functional theory. The electronic structure is first calculated, showing that the hole states are denser than the electron states. Fourier transforms of the time resolved energy levels show that the hot carriers couple to both acoustic and optical phonons. At higher temperature, more phonon modes in the high frequency range participate in the relaxation process due to their increased occupation number. The phonon-assisted hot carrier relaxation time is predicted using non-adiabatic molecular dynamics, and the results clearly show a temperature-activation behavior. The complex temperature dependence is attributed to the combined effects of the phonon occupation number and the thermal expansion. Comparing the simulation results with experiments, we suggest that the multiphonon relaxation channel is efficient at high temperature, while the Auger-like process may dominate the relaxation at low temperature. This combined mechanism can explain the weak temperature dependence at low temperature and stronger temperature dependence at higher temperature.
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Hua Bao, Bradley F. Habenicht, Oleg V. Prezhdo, Xiulin Ruan, and Xianfan Xu "Temperature dependence of hot carrier relaxation in PbSe nanocrystals: an ab initio study", Proc. SPIE 7411, Nanoscale Photonic and Cell Technologies for Photovoltaics II, 741106 (20 August 2009);

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